I bottled a Saison a few weeks ago, and I have had to geyser on me when I opened them. They were both in shorty bottles and had about 1/2" of headspace in them when I cracked them. The kit came with a pre-measured mix of corn sugar and DME for priming. I am worried that I may have too much priming sugar due to and error when the mix was measured. By the way, I was DEFINITELY at FG when I bottled. It didn't change for a week and finished right where the kit said it should. The beer does taste good too.

More head space will make for less CO2 in the beer because more of it will go into the head space. 1 inch to 1/2 inch is not a huge difference but it is noticeable. I doubt it it the cause of your foam overs.

I probably sound like a complete newb since this is the first time I've run into this despite the fact that I've been brewing for a few years now. At the time of this posting I put a long neck in the fridge and just cracked it. No mad crazy foam explosion at all. I think I just need to be careful with the shorties. At least it wasn't a "I think I contaminated my beer!" post.